This invention relates to the field of component handling "pick and place" machines which pick up electronic components such as integrated circuit chips, resistors, capacitors and the like and place these components at predetermined locations on a printed circuit board. The invention more particularly relates to a pick and place machine having a suction head for picking up electronic components and positioning the components on printed circuit boards. The invention also relates to an electronic component feed device which accurately supplies the components to various pick-up locations where the components are picked up by the pick-up head of the pick and place machine.
Pick and place machines are used in electronic device assembly lines for precisely placing electronic components on printed circuit boards at particular predetermined locations. These pick and place machines generally comprise an arm which spans a printed circuit board conveyor belt comprising part of the assembly line. Opposite ends of the arm are movably supported on two tracks which run parallel to but on opposite sides of the conveyor belt so that electric motors can drive the arm back and forth along the conveyor belt. An electronic component pick-up head, which can grasp and release electronic components, is mounted on the arm and driven by electric motors up and down as well as back and forth along the arm. A computer controls the operation of the head to pick up and release components. The computer also controls the motors which drive the head and arm in the three orthogonal directions. Thus, the pick and place machine can be programmed to pick up an electronic component at a predetermined pick-up location, move the component to another predetermined location on a printed circuit board and then release the component at this latter position.
Previously known pick and place machines usually have a pick-up head which includes a flat bottom suction tip and two sets of alignment jaws. The suction tip is used to pick up an electronic component from a component feed device which supplies components to a pick-up location. Because the suction tip usually has only one suction hole located at the flat bottom end of the tip, conventional pick-up heads cannot pick up components which have an uneven upper surface. The uneven surface would prevent the suction tip from making an airtight connection with the component.
The component feed device positions the component to be picked up on the pick-up location to an accuracy of about +0.1 inch. After the suction tip picks up the component, the alignment jaws on the pick-up head then more precisely align the component. Since the jaws must align the component on the suction tip to within about +0.0005 inch to enable the pick-up head to properly position the component on the pads of high density printed circuit boards, these jaws must be manufactured to very high tolerances. Thus, each pick-up head is a relatively expensive piece of equipment.
Furthermore, different size jaws are required for different size components. This is because the smaller jaws cannot open wide enough to grasp the larger components and the large jaws are not delicate enough to fit between and to place small components on the board. Therefore, each jaw-type pick-up head must be replaced with one of a different size every time a different size component is to be picked up and placed on the board. Previously known pick and place machines can be programmed to automatically move to a head change location, disconnect one pick-up head and reconnect a different size head, when required. However, this head changing procedure usually takes about ten seconds. While a single head change will not use up a lot of time, if the head must be changed repeatedly the procedure can be very expensive because it can significantly decrease the output of the assembly line.
These previously known jaw-type pick-up heads have the advantageous characteristic that there is no need for the electronic component feed devices to precisely prealign the electronic components at the pick up location. Provided that the electronic components are prealigned to within about .+-.0.25 inch by the component feed device, the prior art suction tip will to be able to pick up the component. The alignment jaws can then precisely center the component relative to the head. However, these devices have serious disadvantages which restrict their applicability in many situations. For example, as previously noted a system which uses these jaw-type pick up heads can be very expensive, particularly if a multiplicity of different sized heads are required. Furthermore, the placement of the jaws at the lateral sides of the components limits how close together the jaws can place the components on the board. Thus, jaw-type pick-up heads may be unable to place small components on very high density printed circuit boards.
The electronic feed devices of conventional pick and place machines comprise a vertically inclined slide member which has one or more parallel electronic component feed channels formed in its surface. The channels are straight and run from the high end of the inclined member to the low end. A number of each type of component is loaded into the upper end of each channel. The components then slide down toward the lower end of the channels. Each channel has a protrusion or stop at its mouth to stop the components from spilling out the bottom of the channels. The location where the lowermost component in each channel stops is the pick-up location for the components in that channel. The lowermost inch or so of each channel is horizontal rather than inclined so that the flat bottomed pick-up tip can make an airtight seal with the flat upper surface of the component at the pick up location. After the pick-up head removes the lowermost component from the feed channel, the next component in that channel slides down to replace it.
To help urge the components down the feed channels toward the pick-up locations, a vibrator is mounted to the vertically inclined member and oriented so that the back and forth motion of the vibrations is parallel to the longitudinal direction of the channels. These vibrations urge the components down the incline in the direction of the vibrations. Nevertheless, even with the vibrations urging the components down the inclined feed channels, each channel must still be somewhat wider than the components which it contains so that the components will not bind in the channel, but will instead be free to slide down the inclined floor of the channel to the pick up location. The width of the channel, however, limits the positional accuracy with which conventional electronic component feed devices can position electronic components at the pick up locations. Usually, each channel must be about 0.2 inch wider than the component which it contains to prevent the component from becoming stuck in the channel. As a component moves down the vibrating feed channel, it tends to migrate randomly from one side of the channel to the other. Thus, the accuracy with which these conventional feed devices can position components at the pick up locations is limited to about .+-.0.1 inch.
Since the tracks supporting the arm of these previously described pick and place machines are located on opposite sides of the printed circuits board conveyor belt, electronic component feed devices have had to be positioned between the tracks and the slide members containing the components have been disposed at a relatively low inclination to avoid the risk of being damaged by contact with the arm in the event that a programming error accidentally directed the arm over the component feed devices. Also, because the high end of the feed channels, where components are loaded into the component feed devices, is positioned between the tracks that support the arm of the machines, an operator must lean over one of the tracks to replenish the supply of components in the channels of the feed devices. This practice can be dangerous if the machine is running because the arm is moved by powerful motors which could drive the arm into the person reloading the feed channels. Thus, to avoid the danger of being hit by the arm, these previous machines generally should be turned off before the operator replenishes the supply of electronic components in the component feed channels. Stopping the machine, however, is obviously undesirable because it decreases the efficiency of the assembly line.
The device of the present invention has been designed to overcome many of the disadvantages associated with these prior art pick and place machines.